Article for welding stainless steel



Patented May 19, 1953 UNITED STATES PATENT" OFFICE ARTICLE FQR WELDING STAINLESSSTEEL Prentiss VilesQBaytown, Tex assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N. J a corporation 7 of Delaware No Drawing. Original application October 23,

1950, Serial No. 191,725. Divided and this application September 10, 1951, Serial No. 245,977

3 Claims.

The present invention is directed towards' a' method for welding ferrous alloys comprising substantially chromium, iron and nickel and referred to in the trade. as stainless steels. cally the invention is directed towardthe prevention of corrosion due to Weldingof stainless steels which frequently manifestsitself as an after effeet when the welded stainless steels are emp i I r This application is a division of Serial No. 191,725, filed October '23, 1950, for Prentiss S. Viles and entitled Method and Article for Welding Stainless Steel. I I

The chromium nickel stainless steels are those containingnickel and chromium plus other elements to a lesser degree. These chromium nickel stainless steels are known as the austenitic chromium-nickel stainless steels, the nickelbeing added in sufficient amount to makethe steels austenitic and. nonmagnetic withimproved ductility and conductiveness over the straight chromium steels.

These austenitic steels are outstanding in their.

resistance to corrosion and oxidation. Because of their excellent physical properties both at low and elevated temperatures they find wide application'in the food, pulp, "paper, textile, dye,chemical, oil. refining and other related industries. A The severe corrosion encountered in theme of these alloys, however, introduces many perplexing prob lems and many uses will demand a selection among the various types of steel available. 1 The corrosion characteristics of the steel are affected not only by themedia in contact with the structural material but by the treatment the steel is given in its fabrication into structural shapes and facilities. In fabricating containers, pipes and various structural shapes and equipment it isne'cessaryto employ welding. During the welding operation the stainless steel may be subjected to temperatures between 800 and l'60'0 F. whether the welding beaccomplished by the oxy-acetylene, atomic hydrogen, or by the electric are methods. When the austenitic chromium nickel steels are subjected"to'temperatures between 800? and 1600 F. as occurs during welding, astructural change is affectedin the steels The carbon migrates out from the solid solution and combines with theychromium to form chromium carbides along the grain boundaries This {effect is known as c r ide"precipitationand-thisaction More specifi- 2 impoverishes the chromium content adjacent to the grain boundaries; this increases the susceptibility to corrosion attack and leads to what is generally referred to as intergranular corrosion at the grain boundaries.

The precipitation of carbide is affected by a number of factors among which is the time the material is held within the critical temperature range. The longer the heat treatment the more carbides precipitate and as the temperature approaches 1200 F. the more undesirable will be the structural, change in the steel. It follows that the higher carbon content steels are more snsceptible to carburization since there'is more carbon available to combine with the chromium.

The problem of carbide precipitation and corrosion .by intergranular attack has been solved in the industry by subjecting the'welded metal to a;

again inpassing through the critical temperatureregion.

Another method of suppressing the formation of chromium carbides in welding involves addition of several of the rare metals such as columbium and the like to the metals to act as stabilizers. These materials combine with the carbon and. prevent or retard the formation of objectionable chromium carbides and thus reduce the tendency to intergranular, corrosion.

The prior art methods in overcoming the formation of chromium carbides in'the welding of stainless steels is expensive in that furnaces for the heat treatment must be provided which may also contribute to the cost of the steel; Too, even with the addition of stabilizer metals, carbideformation may be encountered.

It is, therefore, the main object of the present invention to provide .a-method of welding austenitic stainless steel alloys which will substantially reduce or prevent the precipitation of chromium-carbides at the grain-boundaries of 3 the metal and thus reduce the susceptibility of the welded material to intergranular corrosion.

In accordance with the present invention the precipitation of carbides during welding operations with its attendant degradation in the quality of the steel is materially reduced or substantially eliminated by the employment of a retarding agent during the welding operation. The carburization retarding agent employed in the present invention is elementary sulfur which is incorporated intothe welding flux and which may be applied to adjacent boundaries of metals which are being welded or may be employed as a coating on the welding rod which is customarily used in weld operations. It is contemplated that the amount of elementary sulfur employed in the practice of the present invention may range from 0.25% to 25% by weight of the welding flux. Lesser quantities give welds which show evidence of carbide precipitation while larger amounts may be impractical.

In order to illustrate the effectiveness of the present invention, a numberof welds were made employing 18-8 steel alloys. Adjacent boundaries of the bodies of the alloys were welded together in accordance with conventional welding techniques. In the first weld a conventional flux was employed. In the following welds a conventionalflux was employed except that amounts ranging from 0.1% to 25% by weight of elementary sulfur was incorporated in the flux and applied to the region of the adjacent boundaries of metals being welded. These welded strips were then tested for intergranular corrosion by the Straus test. The 'Straus test consists of immersing the specimens in boiling Straus solution (3% cupric sulfate, 10% sulfuric acid and 87% distilled water) for '72 hours and then bending the specimen 180. The Straus test is 'a method for determining the extent of carbide precipitation in-metals and a description thereof may be found in the Welding'I-landbo'ok, 1938 edition, American Welding Society, N. Y. pages 533-4.

The following table shows the condition of thev several. welds after testing for metal loss in the Straus test.

Table Straus Test72 Hours Wt. Percent Sulfur Metal 7 in Flux Loss, Condition After 180 Bend Percen O 1. 97 Broken, granular cracks. 0. 1 0. 01 Do.

0.25 0.01 Fair, some visible cracks. '0. 0.01 Good, no cracks.

1.0 0.01 vDo. 7. 0 0, 01 D0. 15. O 0. 01 Do 25.0 0. 85 Do.

1 American Iron and Steel Institute.

The data presented in the foregoing table show that the employment of sulfur in the welding flux duringwelding operations effectively in-.

.4 Straus test that elementary sulfur in the amounts stated in the welding flux effectively inhibits carbide formation and precipitation of carbides at the grain boundaries of the alloys and, therefore, substantially reduces susceptibility to intergranular corrosion.

The mechanism of the precess is not fully understood; however, it is postulated that sulfur and sulfur compounds inhibit metallic carburization and metal carbide formation; thus, chromium carbide is never formed in the'process and, therefore, there are no chromium lean areas in the alloy after Welding, this allows the alloy to retain its original corrosion resistant char- "acteristics.

The welding fluxes to which the sulfur is added are the welding fluxes commonly used in welding stainless steels. Usually these welding fluxes are composed of some compound of the silicates, oxides, hydroxides, halides, carbonates, etc. of magnesium, calcium, sodium, potassium, lithium, and other alkali or alkaline earth metalsalo'ng with small amounts of salts of titanium, manganese, columbium, vanadium, etc.

The welding fluxes mentioned above may have elementary sulfur in an amount in the range from 0.25% to 25 by weight incorporated therein and then applied either to the welding rod or to the region being welded. It is contemplated and may be preferred that the welding flux containing elementary sulfur may be applied as a coating to welding rods in a weight ratio of welding flux coating on the welding rod in the range from 1:2 to 1:4 parts by weight.

The welding rods employed in the practice of thepresent invention may have a composition substantially'the same'as the stainless steel "being welded. It may be preferred under some conditions, however, that the welding rods contain higher proportions of nickel and/or chromium than the alloy being welded. For example, when welding 18-8 steel it may be desirable to use 18-8 welding 'rods coated with a welding flux in accordance with the present invention or use 19-9 or 25-20 welding rods. A welding rod of 18-8 or 19'9 stainless steel having a coating of 1 part by weight of welding flux of the type illustrated to 2 parts by weight of welding rod gives quite satisfactory results in the present invention.

When employing 'a flame in the welding operation the gases may be acetylene or the liquefied petroleum gases, such as propane, butane, butylenes, propylene, mixtures thereof, and the like.

While the oxy-acetylene torch may be used in the welding operations, the invention is equally applicable to electrical arc welding technique since most steels and alloys of the type mentioned above contain carbon which allows the formation of carbides in the welding operation. The invention is also applicable to Welding using atomic hydrogen as a source of heat.

The nature andobjects of the present invention having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is: I

1. An article suitable for use in welding. a ferrous alloy comprising nickel, chromium. and iron which comprises a welding rod of nickel, chromium and iron, having a coating of a welding flux in an amount in the range between 99.75% and by weight and elementary sulfur in an amount in the range between 0.25% and 25 by weight, the weight ratioof said. coat to said rod being in the range between about 1:2 to 1:4;

flux which contains at least 0.25% by weight of elementary sulfur, the weight ratio of said coat to said rod being in the range between about 1:2 to 1:4.

PRENTISS S. VILES.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date Coleman May 22, 1900 Austin July 24, 1934 Jones Feb. 18, 1941 Wasserman Oct. 10, 1944 FOREIGN PATENTS Country Date Great Britain Aug. 12, 1909 

1. AN ARTICLE SUITABLE FOR USE IN WELDING A FERROUS ALLOY COMPRISING NICKEL, CHROMIUM AND IRON WHICH COMPRISES A WELDING ROD OF NICKEL, CHROMIUM AND IRON, HAVING A COATING OF A WELDING FLUX IN AN AMOUNT IN THE RANGE BETWEEN 99.75% AND 75% BY WEIGHT AND ELEMENTARY SULFUR IN AN AMOUNT IN THE RANGE BETWEEN 0.25% AND 25% BY WEIGHT, THE WEIGHT RATIO OF SAID COAT TO SAID ROD BEING IN THE RANGE BETWEEN ABOUT 1:2 TO 1:4. 